Adhesive composition

ABSTRACT

The invention relates to an adhesive composition comprising hydrophilic silicone elastomers and hydrophobic silicone elastomers and optionally water absorbent material, wherein the ratio between the hydrophilic silicone elastomers and the hydrophobic silicone elastomers is from 95:5 to 5:95. The adhesive is suited for medical use due to its skin-friendliness. The invention further relates to a medical device comprising said adhesive composition.

This is a nationalization of PCT/DK2004/000584 filed 2 Sep. 2004 andpublished in English.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to an adhesive composition and a medical devicecomprising an adhesive composition.

2. Description of the Related Art

Medical devices, such as wound care devices and ostomy appliances maycomprise adhesives for direct contact with the skin. It is importantthat the adhesive is skin-friendly, as the skin often is damaged or justextremely fragile, especially when handling chronic wounds. Differentsuitable adhesives are known in the art. Hydrocolloid adhesives areoften used, due to their permeability and good absorption properties.Acrylic adhesives may also be used, especially for thin applications, asthe permeability is low.

Silicone adhesives are very skin-friendly and very suitable for donatingactive agents, such as in medicated patches, but they are also ratherocclusive and hydrophobic, which is a mayor disadvantage for a productbeing worn for prolonged period, such as wound dressings, ostomyappliances or incontinence devices.

Attempts have been made for preparing a more hydrophilic siliconeadhesive. However, these adhesives tend to be difficult to remove due toa higher tack and lower cohesion, and are thus not very useful forapplication to fragile or damaged skin.

Another drawback connected to the use of silicone adhesives is the poorabsorption properties. This problem may be solved by incorporatingabsorbent material e.g. in the form of super absorbent particles.

International patent application No. WO 02/087642 discloses an adhesivecomprising a hydrophilic phase and a hydrophobic phase. The hydrophobicphase may be a silicone elastomer and the hydrophilic phase may be awater absorbing mixture of hydrophilic polymers of non-silicone origin.

In International patent application No. WO 02/076519 is disclosed asilicone-based moisture absorbing matrix for wound care products. Thesticky matrix comprises silicone, gelling agent and optionally asilicone resin. Both silicone compounds are hydrophobic and thereference is silent with respect to the use of hydrophilic silicone.

SUMMARY OF THE INVENTION

The object of the present invention is to provide an adhesivecomposition, being skin-friendly and at the same time having goodpermeability properties.

Another object of the invention is to provide a silicone adhesive withabsorption properties.

Yet another object of the invention is to provide a skin-friendlyadhesive with a good cohesion to the skin and yet easy to remove.

Still another object of the invention is to provide a skin-friendlyadhesive that reduces cell-stripping when removed from the skin.

Still another object of the invention is to provide an adhesive withgood cohesion.

DETAILED DESCRIPTION OF THE PRESENT INVENTION

The invention relates to an adhesive composition comprising hydrophilicsilicone elastomers and hydrophobic silicone elastomers and optionallywater absorbent material, wherein the ratio between the hydrophilicsilicone elastomers and the hydrophobic silicone elastomers is from 5:95to 95:5.

The ratio between the hydrophilic silicone elastomers and thehydrophobic silicone elastomers may be from 10:90 to 90:10, preferably20:80 to 80:20, more preferred 30:70 to 70:30 and most preferred 40:60to 60:40.

Preferably, the ratio between the hydrophilic silicone and thehydrophobic silicone is from 10:90 to 40:60, more preferably from 20:80to 30:70.

In one embodiment of the invention the ratio between the hydrophilicsilicone and the hydrophobic silicone is from 5:95 to 50:50. In anotherembodiment of the invention ratio between the hydrophilic silicone andthe hydrophobic silicone is from 95:5 to 50:50.

The ratio may in one embodiment of the invention be 25:75.

In another embodiment of the invention, the ratio between thehydrophilic silicone and the hydrophobic silicone is from 90:10 to60:40, more preferably from 80:20 to 70:30.

In a preferred embodiment of the invention the ratio is 75:25.

By mixing hydrophobic silicone and hydrophilic silicone into an adhesivecomposition the interaction between the two groups of polymers areoptimal, due to their related nature, compared to mixtures ofhydrophobic silicone and other hydrophilic polymers than silicones.

Silicones such as trimethylsilyloxane terminated polydimetylsiloxane,are hydrophobic. These have an advantage of being inert to hydrophilicsubstances, which means that these substances are not dissolved insilicone and therefore are able to migrate out of the silicone. Thisexplains why silicone is a good as drug release matrix.

For the purpose of this invention we need a silicone that is relativelyless hydrophobic than trimethylsilyloxy-terminated polydimetylsiloxanebut still can be used as a PSA (pressure sensitive adhesive) adhesive.

Hydrophobic silicones can be made hydrophilic by replacing some of themethyl groups along the chain or the chain ends with hydrophilicmoieties well-known to those skilled in the art, such moieties may beoxymethylene and/or oxypropylene, acrylate amide, amines imines etc. Thehydrophilicity or hydrophobicity may also be adjusted to the desiredvalue by radio frequency or electrical current phase plasma treatment orcorona treatment of the silicone fluid stream that passes into a chamberwhere plasma or corona is generated, and that or these monomer moietiesthat renders hydrophobic silicone hydrophilic is/are introduced.

Hydrophilic silicones capable of absorbing small amounts of water areknown. An example may be Silicone 4000 series produced by DOW Corning.The water absorption may be further increased by incorporatingwater-absorbing material such as CMC or cross-linked acrylates. However,such silicone adhesive has low cohesiveness and is thus unsuitable inuse for medical devices.

It has surprisingly been shown that the cohesiveness of the siliconeadhesive may be increased by combining hydrophobic and hydrophilicsilicone.

As a measure of the right combination of the amount of hydrophobic andhydrophilic silicone providing an adhesive composition with an optimaltotal hydrophilicity the surface energy can be used. The surface energyof the composition according to the present invention, measured in termsof water-in-air contact angle for a fully cured silicone mixture againsta glass plate, without the absorbing agent and other ingredientsmentioned in examples below, is preferably between 65 and 105 degree,more preferred between 75 and 100 degree and most preferred between 80and 95 degree.

The surface energy can be measured by the water-in-air contact anglemethod known in the art, where the angle between a drop of distilledwater and the surface of the substrate is measured.

To supplement contact angle findings, surface energy is also determinedfrom the chemical structure of the silicone mixtures using the surfaceand interfacial tension of polymers, oligomers, plasticizers, andadditives involved in the composition. These data are available inpolymer handbooks.

The cohesiveness of the adhesive of the present invention is importantwhen the adhesive has to be removed from a skin or wound site. Lowcohesiveness may result in adhesive residues left on the skin or woundsite or in the areas surrounding the wound site, and/or trauma whileremoving the adhesive due to a high peel force.

The ratio that suits both water absorption and gel cohesiveness may alsoinfluence the peel force of the PSA to be achieved.

The actual peel span of silicone elastomers lies between over 70 N for a100% hydrophilic elastomer to around 0.5 N for 100% hydrophobicelastomer.

The peel force of the adhesive of the present invention may be from 1 Nto 20 N measured according to 180 degree method DS/EN/28510-2.

In order for an adhesive composition to be suitable for medical use itis preferred that the peel force between 1 N and 10 N, more preferablythe peel force is from 1 N to 5 N.

Peel force and gel cohesiveness can be influenced by varying the ratiobetween the hydrophilic and the hydrophobic silicone. Furthermore, thepeel force may be further adjusted by incorporating some otheringredients such as kaolin, crystalline silica magnesium oxide, calciumcarbonate or other reinforcing fillers, plasticisers, such as a lowmolecular silicone oil, e.g. hexamethylene disiloxane, soya bean oil orthe derivative thereof, castor oil or the derivative thereof, or otheradditives known to persons skilled in the art.

Examples of additives may be UV stabilizers such as those known undertrade name “Irganox, Cyanox, Hostanox”, antioxidants, and cross-linkingagents such as peroxides, divinylbenzene. Other suitable compounds maybe acrylic or vinyl ended silicone moieties having an average molecularweight ranging 100 to 10,000. These moieties are also referred to ascross-linking agents. Adhesion promoters may also be added to thesilicone mixtures in order to improve the affinity of the siliconeadhesive for the substrate onto which the adhesive is to be applied. Theadhesion promoters may be silicone based, such as those commercializedby Dow Corning under the name “Silane Z-603”. Titan based such thosecommercialized by Du Pont under the name “Tyzor AA 105” may also beused. Adhesion promoters can be mixed into the silicone compositionprior to coating and curing, or simply used as a primer onto thesubstrate carrier prior to coating.

Silicone adhesives are typically composed of two main components, asiloxane polymer and a silicate resin. Silicone adhesives are eithersupplied pre-cross linked, supplied in a hydrocarbon solvent or in asilane solvent. Or as a two-part system where the first part comprises across-linking agent and the other part comprises a catalyst that in mostcases is an organometallic catalyst, typically an organoplatinumcatalyst.

Examples of suitable silicones for the present invention may bepolydimethyl-siloxane, polymetyiphenylsiloxane, alkylsiloxane,alkyoxysiloxane. An example of a suitable silicate resin may betrimetylsiloxy silicate, also known as tetrakis silicate.

Preferred silicones may be polyorganesiloxane such aspolydimethylsiloxane, poly(oxymethylsilylene), poly(oxyethylsilylene) ormixtures thereof, and/or silicones corresponding to general formulashown below:

R-[Si(2R)-O-Si(2R)-] where R can generally be a methyl and/or ethylgroup or can be substituted by one or several of the following groups—NH2, epoxy, acrylate, metacrylate, acrylamide, ethylene glycol,propylene glycol, halide (Cl, Br, F), maleic anhydride. The degree ofsubstitution can vary from 0 to 90% preferably from 5 to 50% and morepreferably from 5 to 20%.

The hydrophilic and the hydrophobic silicone may be based on the samesilicone elastomer, or they may be based on different siliconeelastomers. By using the same type of elastomers the mixing of the twoelastomers may be facilitated.

In one embodiment of the invention the hydrophilic silicones may besilicones sold by Dow Corning under the name BIO-PSA, the series 7-4000are most preferred. Other silicones such as those known as RTV (roomtemperature vulcanisable) may also be used when rendered lesshydrophobic using the grafting techniques known in the art.

The hydrophobic silicone may preferably be RTV silicones, such as thosesold by Dow Corning, in a preferred embodiment of the invention theseries 7-9000. Other silicones may be suitable.

The molecular weight of the silicone elastomers should be in the rangeof 50,000 to 1,000,000, preferably from 100,000 to 500,000, and morepreferably from 50,000 to 250,000. The molecular weight of thehydrophobic and the hydrophilic elastomers may be essentially the same.

In one embodiment the molecular weight of the hydrophilic siliconeelastomer is considerably smaller than the molecular weight of thehydrophobic silicone elastomer.

In a further embodiment of the invention the adhesive may be in the formof a foam.

The foam may be obtained by promptly releasing the pressure ofpressurized cured silicone adhesive while it is still hot.Pressurization and nitrogen, and carbon dioxide may also be used tocontrol the structure of the foam. Other blowing agents well known inthe art may also be used in order to control the foaming time as well asthe foam structure. By foaming the adhesive of the present invention asilicone adhesive with a better MVTR (moisture and vapor transmissionrate) is achieved, and furthermore, the adhesive obtains cushioningeffect too. These two characteristics may also be obtained by mixingwater-soluble particles into the silicone composition, after curing ofthe adhesive; these particles are leached in the water, leaving smallcraters, through which a better MVTR may be obtained. Another way ofincreasing the MVTR is mixing a fluid into the silicone composition; thefluid has a low boiling point and is not immiscible with silicone. Aftercoating and curing, the immiscible fluid lies within the coating as amicro droplets. The micro droplets of low boiling points fluid areevacuated by vacuum. The resulting adhesive will be in the form of amicroporous mass with improved MVTR.

The composition of the present invention may optionally comprise waterabsorbent material. The incorporation of absorbent material may increasethe absorbency and the MVTR of the adhesive.

The initial absorbency of the adhesive of the present invention may beincreased by the addition of water absorbent material.

The water absorbent material may be in the form of particles or fibers.

The water absorbent material is preferably selected from the group ofcarboxy methyl cellulose (CMC) such as those sold by Hercules under thetrade name Aquasorb® or cross-linked polyoxyethelenes, polyoxpropylenes,polyoxy (ethylene-propylene), such as those commercialized by VeramatrixA/S, under the generic name Versabeads®, or crosslinked polyacrylates,known as super absorbing particles (SAP), such as those sold by Atofinaunder the trade name Norsocryl®, acrylates, alginates, chitosans,polysaccharides and derivatives or mixtures thereof.

The adhesive of the present invention is especially suitable foradhering to the skin or mucous of a living being, such as a human. Theadhesive is skin-friendly, provides a good tack, high flexibility,softness, permeability and is easy to remove. The adhesive may besuitable as a medical adhesive in medical devices, such as wounddressings, ostomy appliances, incontinence devices and other situationswhere a highly skin-friendly adhesive is desired.

The invention further relates to a wound care device comprising anadhesive composition comprising hydrophilic silicone elastomers andhydrophobic silicone elastomers and optionally water absorbent material,wherein the ratio between the hydrophilic silicone elastomers and thehydrophobic silicone elastomers is from 5:95 to 95:5.

Still further, the invention relates to an ostomy device comprising anadhesive composition comprising hydrophilic silicone elastomers andhydrophobic silicone elastomers and optionally water absorbent material,wherein the ratio between the hydrophilic silicone elastomers and thehydrophobic silicone elastomers is from 5:95 to 95:5.

Materials and Methods

Hydrophilic silicone resin from Dow Corning sold under the trade nameBIO-PSA 7-4300.

Hydrophobic silicone resin from Dow Corning sold under the trade namesilicone 7-9800. Silicone 7-9800 is a two parts system with a componentA comprising a catalyst and a component B comprising a cross-linkingagent.

CMC

Acrylate polymer from Atofina sold under the trade name Norsocryl XFS.

Versa-beads-O from Versamatrix

Versa-beads-A from Versamatrix

Versa-beads-E from Versamatrix

N-hexane

Hexamethyldisiloxane

EXAMPLE 1 Preparation of Adhesive

100 parts of BIO-PSA 7-4300 were dissolved in 40 parts of n-hexane understirring at room temperature for 20 minutes. 50 parts of silicone 7-9800(component A and B in a one to one ratio) were added and the mixture wasstirred for another 5 minutes, 20 parts of CMC were then added. Themixture was stirred for 3 minutes. From the mixture a 500 microns filmwas coated on a polyurethane film having 350 microns in thickness. Afterthe n-hexane has evaporated, strips of 10 cm in length and 2 cm in widthwere cut and peel force test at 180 deg. was performed and an averagepeel force of 2.5 N was measured. Test of water uptake was alsoperformed and an absorption of 800 gsm. (gram per square meter) after 24hours was determined.

The adhesive was applied on to human skin and showed no cell strippingafter removal, compared to a conventional adhesive.

EXAMPLE 2 An Ostomy Device

Same as Example 1, except that CMC was replaced by 20 parts of NorsocrylXFS. n-hexane was replaced by 40 parts of HMDS (hexamethylenedisiloxane). A peel force of 1.8 N was determined according to themethod described in Example 1, and a water uptake of 3400 gsm. after 24hours was measured. The adhesive was used for attaching an ostomy devicedirectly to the skin. After removing of the device no traces of skinirritation or cell stripping was noticed.

EXAMPLE 3 An Urine Collecting Device

Same as Example 1 except that more Pt based catalyst was added, by usingsilicone 7-9800 where component A and B were in a ratio 60:40 . . . 7.6N in peel force were obtained when the composition was cured for atleast 24 hours at 40° C., and 7 N when the composition was cured for atleast 24 hours at 80° C. The adhesive was used for attaching a urinecollector to male genital organ, the adhesive provided a tight andleakage proof fit and the patient suffered no pain while removing thedevice.

EXAMPLE 4 Hydrophilic Silicone Adhesive with CMC

100 parts of BIO-PSA 7-4300 was dissolved in 40 parts of n-hexane understirring at room temperature for 20 minutes. 20 parts of CMC were thenadded. The mixture was stirred for 3 minutes. From the mixture a 500microns film was coated on a polyurethane film having 35 microns inthickness. After the n-hexane had evaporated, strips of 10 cm in lengthand 2 cm in width were cut and peel force was determined at 180 deg. Apeel force of 14.8 N was obtained. Water uptake was also measured byimmersion in water and an absorption of 1162 gsm per 24 hours (gram persquare meter) was found. After 24 hours the adhesive began to decomposedue to the lack of cohesiveness of the adhesive.

EXAMPLE 5 Hydrophilic/Hydrophobic Silicone with CMC

70 parts of BIO-PSA 7-4300 was dissolved in 40 parts of n-hexane understirring at room temperature for 20 minutes, and mixed with 30 parts ofsilicone 7-9800. 20 parts of CMC were then added. The mixture wasstirred for 3 minutes. From the mixture a 500 microns film was coated ona polyurethane film having 35 microns in thickness. After the n-hexanehad evaporated, strips of 10 cm in length and 2 cm in width were cut andpeel force was determined at 180 deg. A peel force of 12.0 N wasobtained. Water uptake was also measured by immersion in water and anabsorption of 1062 gsm per 24 hours (gram per square meter) was found.After 24 hours the adhesive was still cohesive and did not dissolve ordisintegrate in the water.

EXAMPLE 6 Adhesive with Improved MVTR Prepared by Use of NaCl

90 parts of silicone 7-9800 were mixed with 5 parts of silicone 7-4300dissolved in n-hexane, then 25 part of CMC were added and the mixturewas stirred for 3 minutes. The mixture was then coated on a PU film,small beads of 1 mm in diameter of NaCl were spread on the surface ofthe coating (NaCl beads covered 25% of the total area), When the coatingwas cured the film was immersed in water for three hours, thusdissolving the beads. The MVTR was increased from 900 gr/m²/24 h(without NaCl treatment) to 1200 gr/m²/24 h (after NaCl treatment).

EXAMPLE 7 Adhesive with Improved MVTR Prepared by Use of Blowing Agent

90 parts of silicone 7-9800 were mixed with 10 parts of silicone 7-4300dissolved in n-hexane, 25 part of CMC were added and stirred for 3minutes. The mixture was coated on a PU film, small beads of 1 mm indiameter made of a mixture of citric acid and backing soda were spreadon the surface of the coating (the beads covered 25% of the total area.When the coating was cured the film was immersed in water for 30 min,and the beads were dissolved. The MVTR was increased from 900 gr/m2/24 hto 1500 gr/m²/24 h.

EXAMPLE 8 Adhesive with Improved MVTR Prepared by Using PEG

95 parts of silicone 7-9800 and 5 parts of silicone 7-4300 dissolved inn-hexane were mixed with 25 part of CMC, and 25 parts of polyethyleneglycol 600 were added and gently stirred to favor the formation ofmicrodroplets, after 3 minutes of stirring. The mixture was coated on aPU film, and cured. When the coating was cured the film was exposed tovacuum for 30 min. The MVTR was increased from 900 gr/m2/24 h to 1100gr/m²/24 h.

1.-11. (canceled)
 12. A method for increasing the MVTR of an adhesivecomposition comprising a hydrophilic silicone elastomer and ahydrophobic silicone elastomer in a ratio (w/w) from 5:95 to 95:5, themethod comprising the addition of sodium chloride to the adhesivecomposition.
 13. The method of claim 12, wherein the adhesivecomposition further contains a water absorbent material.
 14. The methodof claim 13, wherein the water absorbent material is either in the formof particles or fibers.
 15. The method of claim 14, wherein the waterabsorbent material is selected from the group consisting ofcarboxymethyl cellulose, acrylates, alginates, chitosans,polysaccharides and derivatives and mixtures thereof.
 16. The methodaccording to claim 12, wherein a mixture of the silicone components inthe adhesive composition has a water-in-air contact angle between 65 and105 degrees.
 17. The method according to claim 12, wherein the adhesivecomposition has a peel force from 1 to 20 N.
 18. The method according toclaim 12, wherein the hydrophilic silicone elastomer is apolyorganosiloxane elastomer.
 19. The method according to claim 12,wherein the hydrophobic silicone elastomer is a polyorganosiloxaneelastomer.
 20. The method according to claim 12, wherein the hydrophilicsilicone elastomer and the hydrophobic silicone elastomer are based onthe same silicone elastomer.
 21. The method according to claim 12,wherein the molecular weight of each of the hydrophilic siliconeelastomer and the hydrophobic silicone elastomer is between 50,000 and1,000,000.
 22. A method for increasing the MVTR of an adhesivecomposition, the method comprising: (a) providing a hydrophilic siliconeelastomer and a hydrophobic silicone elastomer in a ratio (w/w) from5:95 to 95:5, and (b) adding sodium chloride.
 23. The method of claim22, wherein the adhesive composition further contains a water absorbentmaterial.
 24. The method of claim 23, wherein the water absorbentmaterial is either in the form of particles or fibers.
 25. The method ofclaim 24, wherein the water absorbent material is selected from thegroup consisting of carboxymethyl cellulose, acrylates, alginates,chitosans, polysaccharides and derivatives and mixtures thereof.
 26. Themethod according to claim 22, wherein a mixture of the siliconecomponents in the adhesive composition has a water-in-air contact anglebetween 65 and 105 degrees.
 27. The method according to claim 22,wherein the adhesive composition has a peel force from 1 to 20 N. 28.The method according to claim 22, wherein the hydrophilic siliconeelastomer is a polyorganosiloxane elastomer.
 29. The method according toclaim 12, wherein the hydrophobic silicone elastomer is apolyorganosiloxane elastomer.
 30. The method according to claim 22,wherein the hydrophilic silicone elastomer and the hydrophobic siliconeelastomer are based on the same silicone elastomer.
 31. The methodaccording to claim 22, wherein the molecular weight of each of thehydrophilic silicone elastomer and the hydrophobic silicone elastomer isbetween 50,000 and 1,000,000.